The present invention relates to a development cartridge, a development device and an image formation apparatus.
As one of electrophotography-type image formation apparatuses, a four-cycle color image formation apparatus has conventionally been known. The color image formation apparatus of this type forms color images by forming four color toner images on a photoreceptor by four development cartridges corresponding to four color toners: yellow; magenta; cyan; and black, and sequentially superimposing these four color toner images on an intermediate transfer belt.
In the conventional four-cycle color image formation apparatus, as disclosed in JP 2001-83800 A shown below, the four development cartridges are generally loaded side by side in circumferential direction in a rotatable development rack. Normally, as shown in FIGS. 7 and 8, a development rack 60 is structured such that its peripheral region is divided into four sections by four blade-like members 64 provided radially around a rotation shaft 62 in a standing posture, and four development cartridges 66 are loaded in respective divided regions. Moreover, in both end portions, of the development rack 60 with each development cartridge 66 loaded therein, disc-shaped retention members 68, 70 for retaining each development cartridge are secured. The retention member 70 has an all-around gear formed in its peripheral portion, and the all-around gear is engaged with a drive gear 72. Consequently, the drive gear 72 transmits drive force to the retention member 70, by which the development rack 60 is rotationally driven.
However, the development rack 60 is heavy as four development cartridges 66 filled with toners of respective colors are loaded therein, and this incurs a possibility that torsion is generated due to transmission of rotational drive force from one end portion. Such torsion may cause parallelism between a development roller of a development cartridge at a development position and a photoreceptor off-balanced. Accordingly, in order to prevent the torsion from being generated, the development rack 60 requires properly high rigidity, and this has prevented reduction in size and weight of the development rack 60.
Moreover, on the lateral surface of the retention member 70, four plate-like development position detection pieces 74 are provided in a standing posture at 90 degrees intervals in circumferential direction. By detecting the plate-like development position detection pieces 74 by a sensor such as photointerrupters mounted on the image formation apparatus itself, each development cartridge can be stopped at a development position (referring hereinbelow to the position where the development roller is in contact with the photoreceptor). However, since the retention member 70 is a large member made of resin, it is difficult to secure component accuracy, and even when the development rack 60 is stopped at the position where the plate-like development position detection pieces 74 are detected, sometimes the position accuracy between the photoreceptor and the development roller cannot be secured. Accordingly, in order to secure the position accuracy, the loading positions of the development cartridges 66 need fine adjustment performed in the state that the development cartridges 66, the development rack 60 and the retention members 68, 70 are assembled, and this operation is time-consuming.
Further, in the case of doing maintenance of a certain component around the development rack in the image formation apparatus, the development rack 60 still remains in the apparatus after all the development cartridges 66 are unloaded, making the maintenance operation difficult to perform.